Samples of bodily fluid such as blood, sweat, urine and saliva may be used to detect the presence of particular compounds, such as drugs, in the body. Known methods of testing such samples for the presence of compounds include immunoassay “strip” testing where an antibody is labelled with a suitable marker, for example a visible marker such as colloidal gold, and drawn along a membrane passing over test regions and a control region impregnated with analyte conjugate substances or other binding substances. The presence of particular compounds in the sample are detected by a visible change occurring in the corresponding region due to the interaction of the labelled antibodies and the conjugate substances resulting in visible lines forming on the membrane in some of these regions. The color formed may be proportional to or inversely proportional to analyte concentration depending on the assay format.
The interpretation of the lines formed by such immunoassay testing has previously been carried out subjectively by an operator comparing the intensity of the test line (or the absence or presence of a line) with that of a control, or reference, line.
U.S. Pat. No. 5,580,794 describes a disposable electronic assay device. For single analytes only one light source and detector is necessary. For two analytes, two sets of light source and detector are necessary and so on.